Plastic pipes are increasingly being used in gas and tap water supply piping. Frequently, plastics are used here that have a so-called shape memory. These plastic pipes are easily deformed and will, after deformation, try to return to their original shape.
Such material characteristics can be found preferably in pipes made of cross-linked polyolefins or of cross-linked polyethylene. These are synthetics having strong spatial cross-linking, such as Classes PE-X or XLPE.
The shape memory makes connecting these pipes into piping easier and simpler. Two plastic pipes can be connected to each other by expanding the joining ends of the plastic pipes and pushing a connecting element, such as a pipe connector, into the expanded ends of the plastic pipes. Due to the shape memory of the plastic pipes, the expanded ends will shrink so that at the end of the shrinking process, the pipe ends firmly grip the corresponding inserted portions of the connecting element and the desired pipe connection has thus been established. All that is necessary for connecting the pipes is expanding the pipe ends and inserting the connecting element into the expanded pipe ends.
For expanding the pipe ends, special devices are used as they are known, e.g., from EP 0 725 908 A1. The devices have a multitude of spreading jaws spreadable in a radial direction. The spreading jaws are pushed into the pipe end to be expanded and spread while expanding the pipe end. Frequently, the expanding process takes places in several expansion steps so that the pipe end is gradually enlarged to the desired expanded dimension.